Hydraulic motor trouble detector and hydraulically driven vehicle

ABSTRACT

A failure detection device for a hydraulic motor according to the present invention comprises a hydraulic pump  3  that is driven by a prime mover  2;  a hydraulic motor  1  for traveling that is driven by hydraulic oil discharged from the hydraulic pump  3;  a transmission  7  that is connected with an output shaft of the hydraulic motor  1  for traveling; a stopping detection device  26  that detects that a traveling vehicle has stopped; a fluid level detection device  35  that detects an oil level in the transmission  7;  and a warning device  39, 40  that issues a warning when the stopping detection device  26  detects that the traveling vehicle has stopped, and also the fluid level detection device  35  detects that the oil level in the transmission  7  has reached a predetermined value La.

TECHNICAL FIELD

[0001] This invention relates to a device that detects a failure of thehydraulic motor installed in the hydraulic drive vehicle such as awheeled hydraulic excavator.

BACKGROUND ART

[0002] Generally, the hydraulic drive vehicle such as a wheeledhydraulic excavator comprises a hydraulic pump and a hydraulic motor fortravelling which is driven by oil discharged from the hydraulic pump.The output shaft of this hydraulic motor is connected with the inputshaft of the transmission, and the rotation of the hydraulic motor istransmitted to the wheels through the transmission. A drain chamber isprovided to the hydraulic motor, and the drain oil from the hydraulicmotor returns to a reservoir via the drain chamber. A seal member isprovided between the drain chamber of the motor and a transmissionchamber of the transmission, in order to prevent the drain oil fromflowing into the transmission chamber from the drain chamber.

[0003] In such a hydraulic drive vehicle as described above, if aforeign body should be ingested by the hydraulic motor, proper operationof the hydraulic motor is impeded and there is a danger that thehydraulic motor may be damaged. If the hydraulic motor is damaged, acopious flow of the discharged oil from the hydraulic pump flows intothe drain chamber and then flows into the transmission chamber,penetrating through the seal member. As a result, the transmissionchamber is filled with the drain oil, and a great resistance comes toact on the transmission so that the travelling performance of thevehicle deteriorates. Moreover, when transmission oil becomes mixed withthe drain oil, the quality of the mission oil may be deteriorated, andthis may exert a negative influence upon the operation of thetransmission.

DISCLOSURE OF THE INVENTION

[0004] The present invention is to provide a failure detection devicefor a hydraulic motor that is capable of detecting abnormal operation ofthe hydraulic motor to respond appropriately an abnormal operationalsituation.

[0005] Moreover, the present invention is to provide a hydraulic drivevehicle which is equipped with such a failure detection device for ahydraulic motor.

[0006] In order to achieve the object described above, a failuredetection device for a hydraulic motor according to the presentinvention comprises a hydraulic pump that is driven by a prime mover; ahydraulic motor for traveling that is driven by hydraulic oil dischargedfrom the hydraulic pump; a transmission that is connected with an outputshaft of the hydraulic motor for traveling; a stopping detection devicethat detects that a traveling vehicle has stopped; a fluid leveldetection device that detects an oil level in the transmission; and awarning device that issues a warning when the stopping detection devicedetects that the traveling vehicle has stopped, and also the fluid leveldetection device detects that the oil level in the transmission hasreached a predetermined value.

[0007] Furthermore, a hydraulic drive vehicle according to the presentinvention comprises a hydraulic pump that is driven by a prime mover; ahydraulic motor for traveling that is driven by hydraulic oil dischargedfrom the hydraulic pump; a transmission that is connected with an outputshaft of the hydraulic motor for traveling; a stopping detection devicethat detects that the vehicle has stopped; a fluid level detectiondevice that detects an oil level in the transmission; and a warningdevice that issues a warning when the stopping detection device detectsthat the vehicle has stopped, and also the fluid level detection devicedetects that the oil level in the transmission has reached apredetermined value.

[0008] Therefore, it is possible for an operator to recognize anabnormal state of the hydraulic motor at an early stage and to take anappropriate countermeasure to the abnormal state.

[0009] It is also acceptable to restrict a driving of the hydraulicmotor for traveling instead of issuing a warning. It is desirable tolower the rotational speed of the prime mover when the abnormal state ofthe traveling motor has been detected. It is also acceptable to preventthe vehicle from traveling upon detection of the abnormal state. In suchan abnormal state, restart of the prime mover may be prevented. Inaddition, a warning may be issued as well.

[0010] It is also possible to disable the warning device from issuingthe warning or to disable a drive restriction upon the vehicle, when theworking state has been detected.

[0011] It is desirable to cancel the above-described control in responseto a reset command. An ignition key switch may issue such a resetcommand.

BRIEF DECSRIPTION OF THE DRAWINGS

[0012]FIG. 1 is a circuit diagram showing the structure of the wheeledhydraulic excavator equipped with the failure detection device for ahydraulic motor according to the first embodiment of the presentinvention.

[0013] FIG.2 is sectional view of a traveling motor to which the presentinvention has been applied.

[0014]FIG. 3 schematically illustrates the details of a controller whichconstitutes the failure detection device according to the firstembodiment of the present invention.

[0015]FIG. 4 is a flow chart showing an example of procedure executed bythe controller.

[0016]FIG. 5 is a circuit diagram showing the structure of the wheeledhydraulic excavator equipped with the failure detection device for thehydraulic motor according to the second embodiment of the presentinvention.

[0017]FIG. 6 schematically illustrates the details of a controller whichconstitutes the failure detection device according to the secondembodiment of the present invention.

[0018]FIG. 7 is a circuit diagram showing the structure of the wheeledhydraulic excavator equipped with the failure detection device for ahydraulic motor according to the third embodiment of the presentinvention.

[0019]FIG. 8 schematically illustrates the details of the controllerwhich constitutes the failure detection device according to the thirdembodiment of the present invention.

[0020]FIG. 9 is a circuit diagram showing the structure of the wheeledhydraulic excavator equipped with the failure detection device for ahydraulic motor according to the fourth embodiment of the presentinvention.

[0021]FIG. 10 schematically illustrates the details of the controllerwhich constitutes the failure detection device according to the fourthembodiment of the present invention.

BEST MODE FOR CARRYING OUT THE INVENTION

[0022] —First Embodiment—

[0023] A wheeled hydraulic excavator that is equipped with a failuredetection device according to the first embodiment of the presentinvention will now be described with reference to FIGS. 1 through 4. Thewheeled hydraulic excavator comprises a wheeled undercarriage upon whichan upper-structure is rotatably mounted, and a working attachment isfitted to this upper-structure. A hydraulic motor 1 for traveling whichis driven by a hydraulic circuit for traveling shown in FIG. 1 isprovided in the undercarriage.

[0024] As shown in FIG. 1, hydraulic oil is discharged from a main pump3 which is driven by an engine, the direction and flow rate of thedischarged oil are controlled by a control valve 4, and then thehydraulic oil is supplied to a traveling motor 1 via a brake valve 6with a built-in counterbalance valve 5. A transmission 7 is connectedwith an output shaft la of the traveling motor 1. The rotational speedof the traveling motor 1 is changed by the transmission 7, and istransmitted to tires 10 through propeller shafts 8 and axles 9. Thus,the wheeled hydraulic excavator is propelled. It should be noted thatthe pressure oil from the main pump 3 is also supplied to a hydrauliccircuit for working which is not shown in the figure, and drivesactuators for working.

[0025] The direction of changeover and operation amount of the controlvalve 4 are controlled by pilot pressure from a pilot control circuit.The traveling speed of the vehicle can be controlled by controlling theamount by which the control valve 4 is operated. The pilot controlcircuit comprises a pilot pump 21, a traveling pilot valve 23 thatgenerates a secondary pilot pressure P1 according to the amount by whichan accelerator pedal 22 is stepped upon, a slow-return valve 24 thatdelays oil returning to the pilot valve 23, and a forward/reverseswitchover valve 25 which is used for selecting forward traveling,reverse traveling or neutral for the vehicle. The forward/reverseswitchover valve 25 is constituted of a solenoid-controlled directionalcontrol valve, and its position is changed over by operating a switchnot shown in the figures.

[0026]FIG. 1 shows the condition with the forward/reverse switchovervalve 25 in its neutral (N) position, and moreover when the travelingpilot valve 23 is not being operated. Accordingly, the control valve 4is in its neutral position, the pressure oil from the main pump 3returns to a reservoir, and the vehicle remains stopped. When theforward/reverse switchover valve 25 is switched to its forward travelingposition (F position) or to its reverse traveling position (R position)by the operation of the switch, and then the accelerator pedal 22 isstepped upon, the secondary pressure P1 according to the amount by whichthe accelerator pedal is operated acts on a pilot port of the controlvalve 4. The control valve 4 is operated by the operation amountcorresponding to the secondary pilot pressure P1. Thus, the dischargedoil from the main pump 3 is led to the traveling motor 1 via the controlvalve 4, a center joint 12 and the brake valve 6, so as to drive thetraveling motor 1. At this time, the leakage oil from the travelingmotor 1 is collected to the reservoir through a drain line (drainchamber) 11.

[0027] When the accelerator pedal 22 is released during the vehicletraveling, the pressure oil from the pilot pump 21 is interrupted by thetraveling pilot valve 23, and its outlet port is connected to thereservoir. As a result, the pressure oil having acted on the pilot portof control valve 4 returns to the reservoir via the forward/backwardswitchover valve 25, the slow-return valve 24 and the traveling pilotvalve 23. At this time, the returning oil flow is restricted by therestriction of the slow return valve 24, so that the control valve 4returns to its neutral position gradually. When the control valve 4returns to its neutral position, the supply of the pressure oil (drivepressure) is interrupted, and the counterbalance valve 5 is thenswitched to its neutral position as shown in FIG. 1.

[0028] At this time, the vehicle continues to progress due to itsinertia force, and the operation of the traveling motor 1 changes overfrom motor action to pump action, in which its B port is its suction(inlet) port and its A port is its discharge (outlet) port in FIG. 1.Flow of the pressure oil from the traveling motor 1 is restricted by therestriction of the counterbalance valve 5 (neutral restriction), thepressure between the counterbalance valve 5 and the traveling motor 1then rises and acts on the traveling motor 1 as brake pressure. As aresult, the traveling motor 1 generates the brake torque to slow thevehicle down. If, during the pump operation, the quantity of oil flowinginto the traveling motor 1 becomes insufficient, the additional oil issupplied from a make-up port 13 thereto. The maximum brake pressure isregulated by relief valves 14 and 15.

[0029] A governor 2 a of the engine 2 is connected with a pulse motor 32via a link mechanism 31, and the rotational speed of engine 2 iscontrolled by rotation of the pulse motor 32. In particular, the enginespeed is increased by the normal rotation of the pulse motor 32, whileit is decreased by the reverse rotation of the pulse motor. Apotentiometer 33 is connected with the governor 2 a via the linkmechanism 31, and this potentiometer 33 detects a governor lever anglecorresponding to the rotational speed of the engine 2. The detectedvalue is input to the controller 30 as a control rotational speed NO.

[0030] Furthermore, the controller 30 is connected with a speed sensor26 that detects the vehicle speed, a pressure sensor 34 that detects thesecondary pilot pressure P1 generated by the traveling pilot valve 23corresponding to the pedal operation amount, a fluid level sensor 35that detects the oil level in the transmission 7, a reset switch 36, andan ignition key switch 37 that is turned on/off according to theoperation of an ignition key, respectively. The fluid level sensor 35 isa limit switch, the limit switch 35 is turned on by a float 35 a whenthe oil level in the transmission reaches a predetermined value La whichis set in advance.

[0031] A power source 38 is connected with the key switch 37, and theelectrical power is supplied to the controller 30 in response to the keyswitch 37 being turned on. Accordingly, the controller 30 implementscalculations as will be described later, to control the rotation of thepulse motor 32 by outputting the control signal to the pulse motor 32and also to control operations of a buzzer 39 and a warning lamp 40(which together are referred to as a warning device) by outputtingcontrol signals thereto.

[0032] Next, the construction of the traveling motor 1 will beexplained. FIG. 2 is a sectional view of the variable displacementtraveling motor 1. As shown in FIG. 2, a plurality of pistons 42 (onlyone of which is shown in the figure) are connected with a flange 41 ofthe output shaft la of the traveling motor 1, along its circumferentialdirection. The pistons 42 are slidably inserted into oil chambers 43 aformed in a cylinder block 43 through piston rings 42 a. The end of thecylinder block 43 comes into contact with a swash plate 44, and theircontacting surfaces mutually define a circular cone shape. The swashplate 44 can be swung or inclined together with the cylinder block 43 inthe direction of the arrow shown in the figure, and the motordisplacement varies according to the swing amount or inclined angle ofthe swash plate.

[0033] An inlet or suction port and an outlet or delivery port of oil,not shown in the figure, are provided in the swash plate and a motorcover 45 which is in contact with the swash plate 44, the suction portand the delivery port extending over half a phase, respectively. And,the pressure oil from main pump 3 flows into the oil chambers 43 athrough the suction port, while the oil from the oil chambers 43 a flowsout to the reservoir through the delivery port. Due to this, the pistons42 are slid within the oil chambers 43 a, and, while the swash plate 44is kept in contact with the cylinder block 43, the output shaft la ofthe motor 1 rotates as a unit with the cylinder block 43 and the pistons42. An input shaft 7 a of the transmission 7 is connected by splineswith the motor output shaft 1 a so that the rotation of the travelingmotor 1 is transmitted to the transmission 7.

[0034] At this time, portions of the pressure oil which is supplied tothe oil chambers 43 a from the main pump 3 leaks into the drain chamber11 through gaps between the mutually contacting surfaces of the swashplate 44 and the cylinder block 43, or gaps between the mutually slidingsurfaces of the pistons 42 and the oil chambers 43 a. This leakage oilreturns to the reservoir via a drain hole 1 a which is provided in thebottom of the motor casing 46, while the oil is prevented from flowinginto the transmission chamber 7 b from the drain chamber 11 by sealrings SR.

[0035] If, at this time, a foreign body, for example, should get intothe mutually sliding surfaces of one of the pistons 42 and causes thepiston 42 to stick in (to contact directly with) the cylinder block 43,the cylinder block 43 rotates while being dragged by the piston 42 andthen, the gap between the cylinder block 43 and the swash plate 44becomes partially increased. Moreover, according to circumstances, thepiston ring 42 a may be damaged, which causes the gap between themutually sliding surfaces to become wider. As a result, a large quantityof the pressure oil from the main pump 3 flows into the drain chamber 11through these gaps, and the oil in the drain chamber 11 may penetratethrough the seal rings SR to flow into the transmission chamber 7 b. Ifthis happens, the oil level in the transmission chamber 7 b rises, andthe resistance that acts on the driving shaft of the transmission 7 mayincrease, as well as the performance of the transmission oil maydeteriorate, which exerts a negative effect on the operation of thetransmission 7.

[0036] In this embodiment, this type of abnormal operation of thetraveling motor 1 is detected with a vehicle speed sensor 26 and a fluidlevel sensor 35, and such abnormal state is responded as follows.

[0037]FIG. 3 is a schematic illustration to explain details of thecontroller 30. When the ignition key switch 37 is turned on, theelectric power is supplied to the controller 30 to start execution ofits processing. A function generator 301 outputs a set signal to a setterminal S of a RS flip-flop 302 when the fluid level sensor 35 isswitched on, that is, when the oil level in the transmission chamber 7 bis equal to or greater than the predetermined value La. The value La, inthis case, is set to correspond to rise of the oil level due to thebreakdown of the motor 1, as described above, so that when the oil levelreaches the value La, it may be determined that the traveling motor 1has broken down.

[0038] When the set signal is input to the set terminal S of theflip-flop 302, the flip-flop 302 outputs a high-level signal from itsterminal Q to change over a switchover circuit 303 to its contact “a”side. When the vehicle speed detected by the speed sensor 26 is equal toor lower than a predetermined value (which may equal zero), in otherwords, when the vehicle has stopped, a function generator 308 outputs aclose signal to close a changeover switch 309. As a result, electricalpower is supplied to a buzzer 39 and a warning lamp 40, so that thebuzzer emits sound and the warning lamp 40 is illuminated.

[0039] When a reset switch 36 is turned on, the reset switch 36 outputsare set signal to a reset terminal R of the flip-flop 302. The flip-flop302 sets low-level in the terminal Q in response to this reset signal,and the switchover circuit 303 is then switched to its contact “b” side.As a result, the supply of electrical power to the buzzer 39 and thewarning lamp 40 is interrupted so that the buzzer sound is brought to ahalt and the warning lamp 40 is extinguished. And, when it is detectedby the speed sensor 26 that the vehicle is traveling, an open signal isoutput to the changeover switch 309 to open the changeover switch 309.Also in this case, the buzzer sound is stopped, and the warning lamp 40is turned off.

[0040] A function by which the engine speed should increase along withincrease of the traveling pilot pressure is set in advance in thefunction generator 304, as schematically shown in the figure. Thefunction generator 304 sets the rotational speed N corresponding to thedetected value P1 from the pressure sensor 34 based upon this function,and outputs this set value N to a switchover circuit 305. When theswitchover circuit 303 is switched to its contact “a” side and also thechangeover switch 309 is closed, the switchover circuit 305 is switchedto its contact “a” side. On the other hand, when the switchover circuit303 is switched to its contact “b” side and also the changeover switch309 is open, the switchover circuit 305 is switched to its contact “b”side. Accordingly, the switchover circuit 305 selects either therotational speed N as set by the function generator 304 or an idlingrotational speed Ni which is set in advance in a rotational speedsetting device 306, and outputs its selected rotational speed to a servocontrol section 307 as a target rotational speed Ny. In the servocontrol section 307, the target rotational speed Ny is compared with thecontrol rotational speed Nθ which corresponds to the amount ofdisplacement of the governor lever as detected by the potentiometer 33,and the pulse motor 32 is controlled so as to bring the controlrotational speed Nθ to match the target rotational speed Ny, accordingto the procedure shown in FIG. 4.

[0041] Referring to FIG. 4, first in step S21, the rotational speedcommand value Ny and the control rotational speed Nθ are read in, andthen the flow of control proceeds to step S22. In step S22, Ny issubtracted from Nθ and the result of this subtraction, i.e. therotational speed differential A, is stored in a memory. In step S23,using a predetermined standard rotational speed differential K set inadvance, it makes a decision as to whether or not |A|≧K. If anaffirmative decision is made, the flow of control proceeds to step S24in which a decision is made as to whether or not the rotational speeddifferential A>0. If A>0, it implies that the control rotational speedNθ is greater than the rotational speed command value Ny, in otherwords, the control rotational speed is higher than the target rotationalspeed, the flow of control then proceeds to step S25 in which a signalfor instructing reverse rotation of the motor is output to the pulsemotor 32 in order to reduce the engine speed. As a result, the pulsemotor 32 is caused to rotate in reverse so that the rotational speed ofthe engine 2 drops.

[0042] On the other hand, if A≦0, it implies that the control rotationalspeed Nθ is lower than the rotational speed command value Ny, that is,the control rotational speed is lower than the target rotational value,a signal for instructing normal rotation of the motor is output in orderto increase the engine speed, in step S26. As a result, the pulse motor32 performs normal rotation to increase the engine speed. If a negativedecision is made in step S23, the flow of control proceeds to step S27to output a motor stop signal. Therefore, the rotational speed of theengine 2 is maintained constant. After the appropriate one of the stepsS25-S27 has been executed, the flow of control returns to the beginningof this flow chart.

[0043] The outstanding features of the operation of this failuredetection device for a hydraulic drive vehicle constructed as describedabove will now be explained in concrete term.

[0044] (1) During Normal Operation of the Traveling Motor

[0045] When the traveling motor 1 is in the normal operating condition,there is substantially no oil flow from the drain chamber to thetransmission chamber 7 b, and the oil level in the transmission chamber7 b remains equal to or less than the predefined value La while vehicleis stopped. Therefore, the switchover circuit 303 and the switchovercircuit 305 of the controller 30 are switched to their contact “b” side,respectively. In this condition, if the forward/backward switchovervalve 25 is switched to forward traveling or to reverse traveling, andalso the accelerator pedal 22 is stepped upon, the traveling pilotpressure P1 is generated in correspondence to the amount by which theaccelerator pedal is operated. The servo control section 307 comparesthe target rotational speed Ny according to this traveling pilotpressure P1 with the control rotational speed Nθ corresponding to thedetected value from the potentiometer 33, and then controls the pulsemotor 32 to bring both rotational speeds to correspond to each other.Therefore, the vehicle is propelled with its engine speed increasing inline with the increase of the amount of pedal operation.

[0046] While the vehicle travels, if the oil in the transmission chamber7 b is churned up by the rotation of the drive shaft of the transmission7, the fluid level sensor 35 may be switched on due to change of the oillevel. Although the switchover circuit 303 is switched to its contact“a” side in response to operation of the fluid level sensor, the warningdevices 39 and 40 will not operate because the changeover switch 309 isopen.

[0047] (2) When Operation of the Traveling Motor Becomes Abnormal

[0048] If the motor piston 42 should get stuck at its sliding portion,by a foreign body having gotten into the sliding portion, a largequantity of delivery oil from the hydraulic pump 3 may flow into thedrain chamber 11 as described above. And, if some of this drain oilshould flow into the transmission chamber 7 b penetrating past orthrough the seal rings SR and the oil level in the transmission chamber7 b should reach the predefined value La, the function generator 301outputs the set signal to the set terminal of the flip-flop 302 so thatthe switchover circuit 303 is switched to its contact “a” side inresponse to a high level signal output from the Q terminal of theflip-flop 302. When the vehicle stops under this condition, thechangeover switch 309 is closed so that warning lamp 40 is illuminated,as well as the buzzer sound being emitted. Accordingly, the operatorbecomes aware of an abnormal state of the traveling motor 1, and is ableto perform an appropriate operation, e.g. to stop the engine, inresponse to such abnormal state of the motor 1.

[0049] At this time, the switchover circuit 305 is switched to thecontact “a” side. Due to this, the engine speed is lowered to its idlingrotational speed Ni, and the motor rotational speed also drops in linewith reduction in amount of the delivery oil from the pump. As a result,the quantity of oil flow into the drain chamber 11 decreases, so that itbecomes possible to minimize the leakage of oil from the drain chamber11 to the transmission chamber 7 b. Moreover, useless consumption offuel can be prevented. It should be understood that the oil collected inthe transmission chamber 7 b can be exhausted through a drain hole notshown in the figures, and thereby it is possible to regulate the oillevel in the transmission chamber 7 b within the predetermined value.

[0050] In the state in which the oil level in the transmission chamber 7b is below the predetermined value La, when the reset switch 36 isoperated, the terminal Q of the flip-flop 302 is set to low level andthen the switchover circuits 303 and 305 are switched to their contacts“b” side, respectively. Due to this, the buzzer sound is stopped andalso the warning lamp 40 is extinguished. Moreover, it becomes againpossible to control the engine speed in accordance with operation of theaccelerator pedal. As a result, when the vehicle is to be transportedupon a trailer for the repair of the traveling motor 1, it is possibleto load the vehicle onto the trailer by driving it under its own power.It should be understood that, instead of operating the reset switch 36,it would also be acceptable to turn off the ignition key switch 37. Ifthe traveling motor 1 is damaged heavily and driving the vehicle underits own power is difficult or impossible, it may be pulled up on thetrailer by engaging the end of a bucket of the hydraulic excavator withpart of the trailer and then actuating hydraulic cylinders for a boom orarm.

[0051] According to the first embodiment as described above, a failureof the traveling motor 1 is detected when the oil level in thetransmission chamber 7 b has reached the predetermined value La whilethe vehicle stops, and then the warning devices 39 and 40 are caused tooperate. Therefore, it is possible for an operator to be made aware ofabnormal operation of the traveling motor 1 at an early stage, and torespond appropriately to such abnormal circumstances. In this case, if aperiod of time is required before the oil level becomes steady, it maybe possible to detect a failure of the traveling motor 1 based on thevalue detected by the fluid level sensor 35 after such a period of time.

[0052] Moreover, the engine speed is lowered to the idling rotationspeed Ni to restrict the drive of the traveling motor 1 when a breakdownof the motor 1 is detected. Therefore, the quantity of oil flow into thedrain chamber 11 is reduced irrespective of operation amount of theaccelerator pedal 22, and it is possible to prevent oil leakage into thetransmission chamber 7 b. In addition, the warning devices 39 and 40continue to be operated and the restriction upon traveling of thevehicle is maintained until the reset switch 36 is actuated or theignition key switch 37 is turned off when the oil level in thetransmission chamber 7 b has dropped to the predefined value La orlower. Therefore, it is possible that an operator is reliably made awareof the abnormal operation in the traveling motor 1. In addition, whenthe restriction upon the traveling of the vehicle has been cancelled,the engine speed can again be increased according to the operation ofthe accelerator pedal and it is possible to load the vehicle upon thetrailer or the like easily.

[0053] —Second Embodiment—

[0054] While, in the first embodiment, the engine speed is lowered tothe idling rotational speed Ni to restrict the vehicle speed during afailure in the traveling motor 1, the vehicle will be prohibited fromtraveling, in the second embodiment. The second embodiment of thepresent invention will now be explained with reference to FIGS. 5 and 6.FIG. 5 is a circuit diagram showing the structure of a wheeled hydraulicexcavator which is equipped with a failure detection device according tothe second embodiment, and FIG. 6 schematically illustrates details of acontroller 30A according to the second embodiment. It should be notedthat the same reference numerals are used for elements similar to thatof FIGS. 1 and 3, and the explanation will focus on the points differenttherefrom.

[0055] As shown in FIG. 5, the line between the traveling pilot valve 23and the slow-return valve 24 can be connected with the reservoir througha solenoid valve 47. The solenoid valve 47 is controlled by a controlsignal from the controller 30A. As shown in FIG. 6, a solenoid 47a ofthe solenoid valve 47 is connected with the changeover switch 309.

[0056] While the vehicle is stationary, in other words, while thechangeover switch 309 is closed, if the switchover circuit 303 isswitched to the contact “a” side due to a failure of the traveling motor1, the solenoid 47 a is excited to switch the solenoid valve 47 to itsposition B. As a result, the pressure oil having acted on the pilot portof control valve 4 returns to the reservoir via the forward/backwardswitchover valve 25, the slow return valve 24 and the solenoid valve 47,and the control valve 4 is driven back to its neutral position. As aresult, the supply of pressure oil to the traveling motor 1 isintercepted, and even if the accelerator pedal 22 is actuated, thevehicle stationary state is maintained. In addition, the warning devices39 and 40 operate, and the engine speed is limited to the idlingrotational speed Ni.

[0057] If, in such condition, the reset switch 36 is actuated, theswitchover circuit 303 and 305 are switched to the contact “b” side,respectively. Accordingly, the solenoid 47 a is demagnetized, and thesolenoid valve 47 is switched to its position A. As a result, thetraveling pilot pressure corresponding to the operation of theaccelerator pedal is made to act on the pilot port of the control valve4, and the supply of the pressure oil to the traveling motor 1 becomespossible.

[0058] According to the second embodiment as described above, when afailure in the traveling motor 1 is detected, the traveling pilotpressure is made to return to the reservoir by the operation of thesolenoid valve 47. Therefore, even if the accelerator pedal 22 isactuated, the traveling motor 1 continues to be prevented from rotating,and thereafter it is possible to prevent further oil leakage into thedrain chamber 11.

[0059] It should be noted that it would also be acceptable toadditionally operate a brake, such as a parking brake. In this manner,it would be possible to ensure the stationary state of the vehicle.Moreover, it would also be acceptable to control the engine speedaccording to the value corresponding to the traveling pilot pressure,instead of limiting the engine speed to the idling rotational speed Ni.In this case, the switchover circuit 305 would become unnecessary.

[0060] —Third Embodiment—

[0061] While, in the first embodiment, the engine speed is lowered tothe idling rotational speed Ni to restrict the vehicle speed during afailure in the traveling motor 1, in addition to this function, theengine 2 is prohibited from restarting, in the third embodiment. Thethird embodiment of the present invention will now be explained withreference to FIGS. 7 and 8. FIG. 7 is a circuit diagram showing theconstruction of a wheeled hydraulic excavator which is equipped with afailure detection device according to the third embodiment, and FIG. 8schematically illustrates the structure of a controller 30B according tothe third embodiment. It should be noted the same reference numerals areused for elements similar to that of the FIGS. 1 and 3, and theexplanation will focus upon the points different therefrom.

[0062] As shown in FIG. 7, a starting motor 48 is connected with thecontroller 30B, and the drive of the starting motor 48 is controlledthereby. As shown in FIG. 8, the ignition key switch 37 is connectedwith the starting motor 48 via a relay 310, and the output terminal ofthe changeover switch 309 is connected with the coil of the relay 310.By this structure, when the switchover circuit 303 is switched to thecontact “a” side according to a failure of the traveling motor 1 whilethe vehicle is stationary, the coil of the relay 310 is supplied withactuating electrical energy so that the relay contact is switched to itscontact “R1” side. As a result, the supply of electricity to thestarting motor 48 is cut, and it is impossible to start the engine 2even if the ignition key switch 37 is turned on.

[0063] When, in such a state, the reset switch 36 is actuated, theswitchover circuit 303 is switched to the contact “b” side, and thesupply of electricity to the coil of the relay 310 is intercepted. Therelay contact is thus switched to the contact “R2” side, which makespossible to restart the engine 2. It should be noted that it would alsobe possible to restart the engine 2, as an alternative to operation ofthe reset switch 36, by a repairman, etc. using some apparatuses tosupply an external signal of some type. In this manner, it would beimpossible for an operator to restart the engine upon his own decision.

[0064] According to the third embodiment, when a failure of thetraveling motor 1 is detected, the engine 2 can not be restarted.Therefore, an operator will not imprudently restart the engine 2 todrive the vehicle, and it is possible to ensure that he makes anappropriate response to the abnormal operation of the traveling motor 1.

[0065] —Fourth Embodiment—

[0066] While, in the first embodiment, the engine speed is limited tothe idling rotational speed when a failure of the traveling motor 1 isdetected, regardless of the traveling state or the working state, in thefourth embodiment, no limitation will be imposed upon the engine speedduring the working state. The fourth embodiment of the present inventionwill now be explained with reference to FIGS. 9 and 10. FIG. 9 is acircuit diagram showing the structure of a wheeled hydraulic excavatorequipped with a failure detection device according to the fourthembodiment, and FIG. 10 schematically illustrates details of acontroller 30C according to the fourth embodiment. It should be notedthat the same reference numerals are used for elements similar to thatof FIGS. 1 and 3, and the explanations will focus on the pointsdifferent therefrom.

[0067] As shown in FIG. 9, a forward/reverse changing switch 49 foroutputting a switching command to the forward/reverse switchover valve25, and a brake switch 50 for outputting an operate command to a workbrake not shown in the figures are also connected to the controller 30C.As shown in FIG. 10, a switchover circuit 311 is connected with theterminal Q of the flip-flop 302, and the switchover circuit 311 isswitched according to a signal from a work detection section 312. Thesignals from the forward/reverse changing switch 49 and the brake switch50 are input to the work detection section 312. The work detectionsection 312 sets the switchover circuit 311 to the contact “all sidewhen the forward/reverse switchover valve 25 is in the neutral positionand also the work brake is being operated, while in other conditions,the switchover circuit 311 is switched to the contact “b” side.

[0068] In other words, the switchover circuit 311 is switched to thecontact “b” in any conditions other than the working state, and theswitchover circuits 303 and 305 are switched to the contact “a” side ifa failure of the traveling motor 1 occurs, to restrict the engine speedto the idling rotational speed Ni. When, in such a condition, theforward/reverse switchover valve 25 is set to the neutral position inresponse to the operation of the forward/reverse changing switch 49, andalso the work brake is operated by the operation of the brake switch 50,the switchover circuit 311 is then switched to the contact “a” side. Asa result, the switchover circuits 303 and 305 are both switched to thecontact “b” side to cancel the restriction of the engine speed.

[0069] According to the fourth embodiment, it is detected as to whetheror not the vehicle has started the work operation according to actuationof the forward/reverse changing switch 49 and the brake switch 50. It ispossible to continue working in the normal manner even when thetraveling motor 1 has broken down since the restriction on the enginespeed is disabled during working. It should be noted that the fourthembodiment can be applied, not only to a system which restricts theengine speed during a failure of the traveling motor 1, but also, in thesame manner, to systems which control the vehicle traveling in otherways, such as by stopping the vehicle traveling, by preventing theengine from restarting, or by causing the parking brake to operate. Inother words, the above restrictions upon traveling may be cancelledduring working.

[0070] It would also be possible for the fluid level sensor 35 to beimplemented, not as a switch, but as a sensor which detects the fluidlevel continuously and outputs a set signal to the flip-flop 302 whenthe oil level exceeds the predefined value La. Moreover, although in theabove described embodiments, the buzzer sound is emitted along with theillumination of the warning lamp 40 when the traveling motor 1 hasbroken down, it would also be acceptable to provide one of the warningdevices. Furthermore, it would be possible to flash the hazard warninglamps which are provided around the vehicle, in order to arouse theattention around the vehicle. Although, upon a failure of the travelingmotor 1, the provision of warning and the restriction of the vehicletraveling have been performed at the same time, it would also beacceptable to perform only one of them. Moreover, although the drivingof the traveling motor 1 is limited during a failure of the travelingmotor 1, driving of other actuators, such as a swing motor, may as wellbe restricted.

[0071] Industrial Applicability

[0072] While a failure detection device for a hydraulic motor has beenexplained in terms of application to a wheeled hydraulic excavator byway of example, it would also be possible, in the same manner, to applythe failure detection device of the hydraulic motor according to thepresent invention to a crawler hydraulic excavator, or to other kinds ofhydraulic drive vehicles.

1. A failure detection device for a hydraulic motor, comprising: ahydraulic pump that is driven by a prime mover; a hydraulic motor fortraveling that is driven by hydraulic oil discharged from the hydraulicpump; a transmission that is connected with an output shaft of thehydraulic motor for traveling; a stopping detection device that detectsthat a traveling vehicle has stopped; a fluid level detection devicethat detects an oil level in the transmission; and a warning device thatissues a warning when the stopping detection device detects that thetraveling vehicle has stopped, and also the fluid level detection devicedetects that the oil level in the transmission has reached apredetermined value.
 2. A failure detection device for a hydraulicmotor, comprising: a hydraulic pump that is driven by a prime mover; ahydraulic motor for traveling that is driven by hydraulic oil dischargedfrom the hydraulic pump; a transmission that is connected with an outputshaft of the hydraulic motor for traveling; a stopping detection devicethat detects that a traveling vehicle has stopped; a fluid leveldetection device that detects an oil level in the transmission; and adrive restriction device that restricts a driving of the hydraulic motorfor traveling when the stopping detection device detects that thetraveling vehicle has stopped, and also the fluid level detection devicedetects that the oil level in the transmission has reached apredetermined value.
 3. A failure detection device for a hydraulic motoraccording to claim 2, wherein: the drive restriction device is arotational speed restriction device that restricts a rotational speed ofthe prime mover, and the rotational speed restriction device lowers therotational speed of the prime mover to a predetermined rotational speedwhen the stopping detection device detects that the traveling vehiclehas stopped, and also the fluid level detection device detects that theoil level in the transmission has reached the predetermined value.
 4. Afailure detection device for a hydraulic motor according to claim 2,wherein: the drive restriction device is a traveling prevention devicethat prevents the driving of the hydraulic motor for traveling, and thetraveling prevention device prevents the hydraulic motor for travelingfrom being driven when the stopping detection device detects that thetraveling vehicle has stopped, and also the fluid level detection devicedetects that the oil level in the transmission has reached thepredetermined value.
 5. A failure detection device for a hydraulicmotor, comprising: a hydraulic pump that is driven by a prime mover; ahydraulic motor for traveling that is driven by hydraulic oil dischargedfrom the hydraulic pump; a transmission that is connected with an outputshaft of the hydraulic motor for traveling; a stopping detection devicethat detects that a traveling vehicle has stopped; a fluid leveldetection device that detects an oil level in the transmission; and arestart prevention device that prevents a restarting of the prime moverwhen the stopping detection device detects that the traveling vehiclehas stopped, and also the fluid level detection device detects that theoil level in the transmission has reached a predetermined value.
 6. Afailure detection device for a hydraulic motor according to claim 2,further comprising: a warning device that issues a warning when thestopping detection device detects that the traveling vehicle hasstopped, and also the fluid level detection device detects that the oillevel in the transmission has reached the predetermined value.
 7. Afailure detection device for a hydraulic motor according to claim 5,further comprising: a warning device that issues a warning when thestopping detection device detects that the traveling vehicle hasstopped, and also the fluid level detection device detects that the oillevel in the transmission has reached the predetermined value.
 8. Afailure detection device for a hydraulic motor according to claim 1,further comprising: a working detection device that detects a workingstate, and a warning control device that disables the warning devicefrom issuing the warning, when the working detection device detects theworking state.
 9. A failure detection device for a hydraulic motoraccording to claim 2, further comprising: a working detection devicethat detects a working state, and a drive restriction control devicethat disables a drive restriction on the hydraulic motor for travelingby the drive restriction device, when the working detection devicedetects the working state.
 10. A failure detection device for ahydraulic motor according to claim 5, further comprising: a workingdetection device that detects a working state, and a restart preventioncontrol device that disables a restart prevention for the prime mover bythe restart prevention device, when the working detection device detectsthe working state.
 11. A failure detection device for a hydraulic motoraccording to claim 1, further comprising: a reset command switch thatresets the warning device.
 12. A failure detection device for ahydraulic motor according to claim 2, further comprising: a resetcommand switch that resets the drive restriction device.
 13. A failuredetection device for a hydraulic motor according to claim 5, furthercomprising: a reset command switch that resets the restart preventiondevice.
 14. A failure detection device for a hydraulic motor accordingto claim 1, wherein: the warning device is reset by actuation of anignition key switch.
 15. A failure detection device for a hydraulicmotor according to claim 2, wherein: the drive restriction device isreset by actuation of an ignition key switch.
 16. A failure detectiondevice for a hydraulic motor according to claim 5, wherein: the restartprevention device is reset by actuation of an ignition key switch.
 17. Ahydraulic drive vehicle, comprising: a hydraulic pump that is driven bya prime mover; a hydraulic motor for traveling that is driven byhydraulic oil discharged from the hydraulic pump; a transmission that isconnected with an output shaft of the hydraulic motor for traveling; astopping detection device that detects that the vehicle has stopped; afluid level detection device that detects an oil level in thetransmission; and a warning device that issues a warning when thestopping detection device detects that the vehicle has stopped, and alsothe fluid level detection device detects that the oil level in thetransmission has reached a predetermined value.
 18. A hydraulic drivevehicle, comprising: a hydraulic pump that is driven by a prime mover; ahydraulic motor for traveling that is driven by hydraulic oil dischargedfrom the hydraulic pump; a transmission that is connected with an outputshaft of the hydraulic motor for traveling; a stopping detection devicethat detects that the vehicle has stopped; a fluid level detectiondevice that detects an oil level in the transmission; and a driverestriction device that restricts a driving of the hydraulic motor fortraveling when the stopping detection device detects that the vehiclehas stopped, and the fluid level detection device detects that the oillevel in the transmission has reached a predetermined value.
 19. Ahydraulic drive vehicle, comprising: a hydraulic pump that is driven bya prime mover; a hydraulic motor for traveling that is driven byhydraulic oil discharged from the hydraulic pump; a transmission that isconnected with an output shaft of the hydraulic motor for traveling; astopping detection device that detects that the vehicle has stopped; afluid level detection device that detects an oil level in thetransmission; and a restart prevention device that prevents the primemover from restarting when the stopping detection device detects thatthe vehicle has stopped, and also that the fluid level detection devicedetects that the oil level in the transmission has reached apredetermined value.